Honeywell MS4103 manual Pressure Drop Correction for Ethylene Glycol Solutions

Appendix A: Valve Selection and Sizing

Water Valves

Determine the capacity index (Cv) for a valve used in a water application, using the formula:

Q G

CV = -------------

h

Where:

Q= Flow of fluid in gallons per minute required to pass through the valve.

G = Specific gravity of the fluid (water = 1).

h= Pressure drop in psi. See Figures 14 and 15 for glycol solution correction values.

NOTE: The calculated Cv will rarely match the Cv of an avail- able valve. For most accurate proportional control, select the valve with the next lower Cv value, and increase the pressure drop across the control valve to achieve the required flow through the coil by reducing the setting of the balancing valve. Otherwise, turn- down ratio will be reduced, proportionally.

For example, if the calculated Cv is 87, and the two closest Cv values are 63 and 100, the best choice for control precision would be the valve with a Cv of 63, and increase pressure drop across the valve by 90%.

If increased pressure drop is not possible, use the valve with Cv of 100, and accept a 13% reduction in valve rangeability.

For two-position control, always chose the largest Cv greater than the coil with acceptable close-off pressure rating.

Determining the Cv of a water valve requires knowing the quantity of water (gpm) through the valve and the pressure drop

(h)across the valve. If the fluid is a glycol solution, use the pressure drop multipliers from either Figure 14 or 15. See the sections on QUANTITY OF WATER and WATER VALVE PRESSURE DROP. Then select the appropriate valve based on

Cv, temperature range, action, body ratings, etc., per VALVE SELECTION guidelines.

	1.6
FACTOR		40%				ETHYLENE
			50% BY MASS
						GLYCOL
						SOLUTION
CORRECTION	1.4
		20%
		30%
DROP	1.2
			10%
PRESSURE	1.0
				WATER
	0.8
	0		40		80	120	160
				TEMPERATURE, F			M12226

REPRINTED BY PERMISSION FROM ASHRAE HANDBOOK—

1996 HVAC SYSTEMS AND EQUIPMENT

Fig. 14. Pressure Drop Correction for

Ethylene Glycol Solutions

FACTOR	1.6
			30%		50% BY MASS	PROPYLENE
						GLYCOL
				40%		SOLUTION
CORRECTION	1.4
		20%
DROP	1.2
			10%
PRESSURE	1.0
					WATER
	0.8
	0	40			80	120	160
					TEMPERATURE, F		M12227

REPRINTED BY PERMISSION FROM ASHRAE HANDBOOK—

1996 HVAC SYSTEMS AND EQUIPMENT

Fig. 15. Pressure Drop Correction for Propylene Glycol

Solutions.

Quantity of Water

To find the quantity of water (Q) in gallons per minute use one of the following formulas:

1.When Btu/hr is known:

				Btu ⁄ hr
				Q = ----------------------
Where:				K ⋅ TDw
Btu/hr=			Heat output.
K	=		Value from Table 3; based on temperature
			of water entering the coil. The value is in
			pounds per gallon x 60 minutes per hour.
TDw	=		Temperature difference of water entering
			and leaving the coil.
Table 3. Water Flow Formula Table
Water						Water
Temp F			K		Temp F		K
40		502			200		484
60		500			225		483
80		498			250		479
100		496			275		478
120		495			300		473
150		490			350		470
180		487			400		465

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